<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>Title</title>
    </head>
    <!--内部js-->
    <script>
        alert("你好")
    </script>

    <body>
   <input type="text">
        <!--外部js-->
        <script src="../../a.js">
        </script>


        <script>
            var a=3;
            alert(a);
            a="abc"
            alert(a);
        </script>

    </body>
</html>